The invention generally relates to rotary drilling heads for the oil industry and more particularly to a rotary drilling head that includes a diamond enhanced bearing assembly which can be retrieved through the rotary table of the drill rig and which increases rotational drilling speeds and lengthens service intervals.
Referring initially to FIG. 1, there is shown a conventional rig 10 for rotating a drill bit 12 on the end of a drill string 14 for drilling a well bore 16. The drilling rig 10 includes a rotary table 18 located on the floor 20 of rig 10 for transmitting torque to the drill string 14. The drill string 14 extends through a blowout preventer (xe2x80x9cBOPxe2x80x9d) stack located beneath the rig floor 20 and includes a kelly 22 at its upper end and a plurality of drill pipes 24 including a plurality of drill collars 26 connected at it lower end to the drill bit 12. The drill string 14 transmits rotational and axial movements to the drill bit 12 for drilling the well bore 16.
Referring now additionally to FIGS. 2 and 3, there is shown a typical kelly 22 having threaded rotary shouldered connections 28 at its top and bottom and a center section 30 with a polygonal outer cross section. The rotary table 18 includes a clearance hole, typically 17.5xe2x80x3 or 22.5xe2x80x3 in diameter, for housing a drive bushing that corresponds to the polygonal geometry 30 of kelly 22 for applying torque to kelly 22. Kelly 22 in turn transmits torque to the drill string 14 and bit 12 at the bottom of well bore 16.
Drilling fluids, often referred to as drilling mud, are pumped downward through the flowbore of the drill string 14 under high pressure, through drill bit 12 and then returns upwardly via the annulus 44 formed between well bore 16 and drill string 14 to remove the cuttings to the surface. The returning mixture of drilling fluids and cuttings is diverted beneath the rig floor 20 to a mud reservoir by means of a device commonly referred to in the industry as a rotary drilling head assembly 46.
A rotary drilling head assembly 46 is typically mounted below the floor 20 of the drilling rig 10 on the top of the BOP stack to redirect the drilling fluid returning from the well bore 16 and to allow rotation and deployment of the drill string 14 through the rotary table 18. During normal drilling operations, the blowout preventers are maintained in the xe2x80x9copenxe2x80x9d position, leaving only the rotary drilling head to divert the returning pressurized drilling fluids away from the rig 10.
FIG. 2 illustrates a typical prior art rotary drilling head assembly 46 having an outer stationary housing or bowl 48 and an inner drive ring 50 with a bearing assembly 52 disposed in between allowing drive ring 50 to rotate within bowl 48. Outer bowl 48 includes a flange 54 for mounting the assembly 46 to the BOP stack and a flow diverter port or outlet 56 having a flange 58 for the attachment of a pipe extending to the mud reservoir. Assembly 46 further includes an inner stripper assembly 60 slidably received within drive ring 50 and connected to the upper end of drive ring 50 by a retaining clamp 62 allowing stripper assembly 60 to rotate with inner drive ring 50. Stripper assembly 60 includes an outer housing 66 bonded by a rubber insert 68 to inner drive bushing 32. The lower end of outer housing 66 is bolted to a flange 64 which is bonded onto stripper rubber 42. A primary non-rotary seal 70 and a secondary non-rotary seal 72 serve to statically seal the outside of stripper assembly 60 from bearing assembly 52 and rig floor 20. Bearing assembly 52 includes an upper set of roller bearings 74 and a lower set of roller bearings 76. Upper and lower roller bearings 74, 76, respectively, are separated axially by a bearing spacer 78. An external pressurized oil system lubricates the bearings 74, 76 through hydraulic quick connects 80, and is maintained by rotary lubrication bearing seal members 82 above and below the bearing assembly 52. Bearing seal members 82 are stationary even while there is full 360xc2x0 rotation of stripper assembly 60 and drive ring 50 within outer bowl 48. Since the clamp assembly clamps the rotating side of the bearing assembly, the clamp assembly must also rotate.
The rotary drilling head assembly 46 counteracts forces due to the upward pressure from the returning drilling fluids, the radial wobble of the drill string 14, and the downward engagement forces of drill string 14. The bearing assembly 52 of a conventional drilling head assembly 46 includes tapered roller bearings to enable rotation of the drive ring 50 with respect to the outer bowl 48 and to overcome these various forces. Previous designs utilize two horizontally opposed tapered roller bearings 74, 76 spaced apart axially to handle the loads encountered during drilling operations, as shown in FIG. 2. Because the design of tapered roller bearings allows them to counteract loads in both the thrust and radial directions, the lower set of bearings 76 encounters the upward annular fluid forces and radial wobble forces simultaneously, while the upper set of bearings 74 encounters the downward drill string and radial wobble forces. This arrangement allows radial and axial forces to be countered regardless of the direction that they may be acting upon rotary drilling head 46.
During operation, individual sections of drill pipe 24 are connected to the upper end of drill string 14 with their upper end attached to the lower end of kelly 22. The new section of drill pipe 24 is then lowered through the stripper assembly 60. As the rotary table 18 rotates, rotary table 18 rotates kelly 22 and thus kelly bushing 34 disposed within drive bushing 32 and around kelly 22. As shown in FIG. 3, drive bushing 34 includes an inside cutout geometry 36, an outside geometry 38, and a split cut 40. Inside geometry 36 corresponds to polygonal section 30 of kelly 22, and outside geometry 38 corresponds to a drive bushing seat 32 of a stripper assembly 60 hereinafter described. Split cut 40 facilitates the assembly and disassembly of drive bushing 34 about kelly 22. Drive bushing 34 is slidably engaged both about polygonal section 30 of kelly 22 and within the corresponding geometry of drive bushing seat 32. Kelly bushing 34 thereby allows kelly 22 to pass through the rotary drilling head 46 while also transmitting torque from the rotary table 18 to the drill string 14 and stripper assembly 60 of the drilling head 46 simultaneously.
Stripper rubber 42 seals with drill string 14 as the drill string 14 moves axially through stripper assembly 60. Kelly 22, drill pipes 24, and threaded pipe connections 28 therebetween may be of many different sizes and shapes and yet must pass through stripper rubber 42. Therefore, the stripper rubber 42 of rotary drilling head assembly 46 must be flexible to sealingly engage and accommodate the various sizes of the components of drill string 14. Rubber stripper 42 also diverts the drilling mud through side port outlet 56 of drilling head 46 in maintaining the sealing engagement with drill string 14.
From time to time the stripper assembly 60 must be removed to replace the stripper rubber 42. This requires disconnecting the retaining clamp 62 to release outer housing 66 of stripper assembly 60. When the outer housing 66 is larger than the opening through the rotary table 18, the stripper assembly 60 must be removed from beneath the rig floor 20 which is expensive.
Further, when service intervals dictate, the bearing assembly 52 must be replaced. This requires that the drilling head assembly 46 be dismantled and the bearing assembly 52 lifted out of outer bowl 48. This is done by removing bearing retaining screws 84 that secure bearing assembly 52 to outer barrel 48. Once removed, bearing assembly 52 can be inspected, replaced or repaired if no longer functioning properly. To prevent disrupting operations with time consuming disassembly procedures, the clearance diameters of rotary table 18 and any other equipment between it and rotary drilling head 46 must be larger than the maximum diameter of bearing assembly 52. If smaller rig floor equipment is used, then rotary drilling head assembly 46 must be removed from beneath the rig floor 20 for disassembly.
One major limitation of prior art rotary drilling head designs is that the roller bearing assemblies require a large radial clearance. Thus, prior art drilling head designs either require a large hole in the rotary table 18 or must be removed from beneath the rig floor 20 for dismantling. It is desirable to produce a rotary drilling head assembly 46 that has a small radial clearance that will allow the stripper assembly 60 and bearing assembly 52 to be removed through the opening in the rotary table 18.
During drilling operations, the seals that maintain the lubrication oil on the drilling head bearing packages may fail prematurely. In the event that a lubrication seal is lost, the roller bearings are destroyed and must be immediately replaced. When seal failure occurs, the entire drilling operation must be stopped so that the rotary head bearing assembly 52 can be replaced. To replace the roller bearings, the whole rotating bead must be removed from the well casing. To prevent costly outages and repair regimens, a more durable bearing design that can function following a lubrication seal loss is desirable to minimize down time.
Diamond bearings are disclosed in U.S. Pat. No. 4,410,054 for use in downhole mud motors. The present invention overcomes the deficiencies of the prior art.
The rotary drilling head assembly of the present invention includes a housing having a bore for receiving a drive member. The drive member has an outer diameter of less than 17{fraction (1/2+L )} inches so as to pass through the 17{fraction (1/2+L )} inch opening in a rotary table. A bearing assembly is disposed between the housing and drive member allowing the drive member to rotate within the housing and includes an outer stationary portion and an inner rotating portion maintained in place by upper and lower threaded retaining rings. Retaining clamps attach the outer stationary portion to the housing and the rotating portion to the drive member. Rotary seal assemblies isolate the bearing assembly and its lubrication system from the drilling fluid to prevent premature wear and failure of the bearing. 
The bearing assembly includes a plurality of opposing disc-like members that have flat bearing surfaces meeting on a substantially planar surface of contact. The disc-like members are preferably made of a polycrystalline diamond material. The highly wear resistant polycrystalline diamond bearing resists drill string and axial loads.
The bearing assembly includes at least two long-lasting diamond bearings to carry axial thrust loads. Each bearing includes annular bearing plates each supporting a plurality of friction bearing members having bearing faces of highly wear resistant polycrystalline diamond to carry the thrust load.
The diamond enhanced bearing of the present invention is more compact than equivalent roller bearing assemblies of the prior art rotary head assemblies. By reducing the space required in the radial dimension, the diamond enhanced rotary drive assembly fits through the opening in, a 17.5xe2x80x3 rotary table which was not possible with the over 20xe2x80x3 diameter roller bearing design of the prior art. Some current roller bearings are small enough to be retrieved through a 17.5xe2x80x3 rotary table but their load carrying capacity is limited by their diminished radial envelope.
Additionally, the diamond enhanced bearing package of the improved rotary drilling head assembly is designed to be symmetrical. In the event that one side of the bearing wears faster than the other, the bearing may be removed and reversed to allow the drilling head to continue in service. Rotary seals are positioned below and above the diamond enhanced bearings of the present invention encapsulating a lubricant fluid that provides lubrication to the bearing members. The use of diamond bearings, however, makes it possible for the bearings to be safely cooled and lubricated by the drilling fluid in the event of a lubrication seal failure.
By incorporating the inherent fail-safe properties of diamond enhanced bearings into the rotary drilling head assembly of the present invention, considerable advances in drilling head life can be achieved. By utilizing a more durable rotary drilling head with a higher maximum rotational speed, production costs can be reduced by both reducing the number of expensive bearing replacement operations and being able to drill at a faster rate than before.
Other objects and advantages of the present invention will become apparent from the following description and claims.